Operating method for a semiconductor component

ABSTRACT

The present invention creates an operating method for a semiconductor component having a substrate; having a conductive polysilicon strip which is applied to the substrate; having a first and a second electrical contact which are connected to the conductive polysilicon strip such that this forms an electrical resistance in between them; with the semiconductor component being operated reversibly in a current/voltage range in which it has a first differential resistance (Rdiff1) up to a current limit value (It) corresponding to an upper voltage limit value (Vt) and, at current values greater than this, has a second differential resistance (Rdiff2), which is less than the first differential resistance (Rdiff1).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of German Patent ApplicationNo. 101 34 665.4 filed on Jul. 20, 2001 the disclosures of which areincorporated by reference herein in their entirety.

DESCRIPTION

[0002] The present invention relates to an operating method for asemiconductor component having a substrate, having a conductive stripcomposed of a semiconductor material which is applied to the substrate,having a first and a second electrical contact which are connected tothe conductive strip such that this forms an electrical resistance inbetween them.

[0003] Although, in principle, any semiconductor components with switchcharacteristics can be used, the present invention and the problems onwhich it is based will be explained with reference to trigger diodesbased on silicon technology.

[0004] Trigger diodes are semiconductor components which switch from ablocking state to a switched-on state when the voltage which is appliedbetween the two connections exceeds a specific value and, in theprocess, greatly reduce their differential resistance. One known type ofa trigger diode is the so-called four-layer diode (Binistor), which issometimes also referred to as a breakover diode and is equally athyristor which has no control electrode but makes use of breakdowntriggering.

[0005] Trigger diodes and other known current and voltage switchablesemiconductor components, such as controlled transistors (JFETs, NMOS,etc.), thyristors, TRIACs and DIACs as well as bipolar transistors forhigh-current pulse shaping have the following disadvantages:

[0006] a. complex multilayer structure;

[0007] b. restricted adaptability of the key parameters within thespecified manufacturing technology;

[0008] c. a high level of development effort, resulting from the complexmethod of operation;

[0009] d. complex and time-consuming process engineering (a large numberof mask levels, etc.);

[0010] e. no compatibility for integration in conventional VLSIprocesses;

[0011] f. lack of stability with respect to technology fluctuations andtransfer to different production sites; and

[0012] g. large area and space requirements in VLSI circuits.

[0013] One object of the present invention is thus to provide anoperating method for a semiconductor component, which can easily beintegrated in a VLSI process, in order to achieve a current-switched orvoltage-switched switch characteristic.

[0014] According to the invention, this object is achieved by theoperating method specified in claim 1.

[0015] The idea on which the present invention is based is to allow theinitially mentioned semiconductor component to be operated reversibly ina current/voltage range in which it has a first differential resistanceup to a first current limit value corresponding to an upper voltagelimit value and, at current values greater than this, has a seconddifferential resistance, which is less than the first differentialresistance.

[0016] The operation, according to the invention, of the component whichis known per se in the form of a strip composed of a semiconductormaterial is distinguished by the simplicity of production, design andintegribility in modern CMOS, BiCMOS and bipolar technologies for thecomponent, and by its excellent linearity in the two operating modes,with a high and a low differential resistance. One excellent feature ofthe novel operation is undoubtedly the full adjustment capability of thekey parameters within one manufacturing technology, just by means oflayout measures, and hence the capability to use a number of suchcomponents, with a different characteristic, in a large scale integratedproduct.

[0017] According to the invention, the known resistance strip is usedreversibly, with a different differential resistance, in two operatingstates. Reversibly relates, by way of example, to non-destructiveoperation in the DC mode or at least in the pulsed mode, with a typicalduty ratio of 1 ms [sic].

[0018] When the current level is low, the resistance assumes a specificnominal value and, when a specific threshold current or a specificthreshold voltage is exceeded, the component switches to a more highlyconductive state, with a lower differential resistance.

[0019] The characterizing parameters of this switchable resistor are thetwo differential resistances Rdiff1 and Rdiff2, the limit voltage Vt,the limit current It and the upper limit of the reversible operatingrange, characterized by the critical current Ik. If required, thecomponent may also have a blocking range up to a threshold value ofVth<Vt.

[0020] The use of the polysilicon resistor according to the inventionhas the following further advantages over the prior art:

[0021] a. simple structure, capability for implementation easily usingall technologies;

[0022] b. full adaptability of the key parameters possible just by meansof layout measures (“custom design”);

[0023] c. simple internal structure linked to a low level of developmenteffort;

[0024] d. short process time;

[0025] e. seamless integribility in conventional VLSI processes;

[0026] f. high stability with respect to technology fluctuations andtransfer to different production sites, by virtue of a robust internalstructure; and

[0027] g. small area requirements in VLSI circuits owing to goodintegribility and the comparatively high current carrying capacity perunit area (the area advantage is a factor of 2 to 10).

[0028] The dependent claims contain advantageous developments andimprovements of the respective subject matter of the invention.

[0029] According to a further preferred development, the strip has asheet resistance which is in the range between 100 and 1000 ohms persquare.

[0030] According to a further preferred development, the strip has acuboid shape with a length l, a width b and a height h.

[0031] According to a further preferred development, the strip is formedfrom a number of strip elements with different dopings and/or lengths soas to produce a predetermined voltage limit value.

[0032] According to a further preferred development, the strip elementsare alternately p-doped and n-doped.

[0033] According to a further preferred development, the alternatedoping creates additional diode forward-bias thresholds in the currentpath.

[0034] According to a further preferred development, the alternatedoping creates additional diode breakdown thresholds in the currentpath.

[0035] According to a further preferred development, the voltage limitvalue Vt is set in accordance with the relationship Vt=R b(k/Rsq)½,where R is the resistance, b is the width, k is a constant and Rsq isthe sheet resistance of the strip.

[0036] According to a further preferred development, the semiconductorcomponent is used as an ESD protective element.

[0037] According to a further preferred development, the semiconductorcomponent is used with two functions, as an ESD protective element andas a bias resistor, in a radio-frequency circuit arrangement.

[0038] According to a further preferred development, the strip is formedfrom doped polysilicon as the semiconductor material.

[0039] Exemplary embodiments of the invention will be explained in moredetail in the following description and are illustrated in the drawings,in which:

[0040]FIG. 1 shows a schematic illustration of a polysilicon resistor ona substrate, in order to explain a first embodiment of the presentinvention;

[0041]FIG. 2 shows the response of the differential resistance and thecurrent/voltage characteristic of the polysilicon strip for the firstembodiment of the operating method according to the invention;

[0042]FIG. 3 shows a current/voltage characteristic with two selectedresistors with the same nominal resistance;

[0043]FIG. 4 shows the arrangement of a polysilicon strip in order toexplain a second embodiment of the operating method according to theinvention; and

[0044]FIG. 5 shows a radio-frequency circuit arrangement in order toexplain one field of application of the operating method according tothe invention.

[0045] Identical reference symbols in the figures denote identical orfunctionally identical components.

[0046]FIG. 1 shows a schematic illustration of a polysilicon resistor ona substrate, in order to explain a first embodiment of the presentinvention.

[0047] In FIG. 1, the reference symbol 1 denotes a silicon wafersubstrate, on which an insulation layer 5, for example composed ofsilicon dioxide, is applied. A cuboid polysilicon strip with a length l,a width b and a height h is provided on the insulation strip 5, and isdenoted by the reference symbol 10. The technological production of sucha polysilicon strip 10 is well known from the prior art. Chemical vapordeposition with subsequent structuring of doped polysilicon may bementioned as one example. With a known technology, by way of example,the height h of the polysilicon resistance strip is about 0.15 μm, thewidth b is in the region of a few micrometers, and the length l is inthe region of a few tens of micrometers.

[0048] The sheet resistance of the deposited polysilicon, and hence theresistance of the polysilicon strip 10, may be varied within a very widevalue range by the doping level, for example using boron, arsenic,phosphorus and the like. Comprehensive investigations have been carriedout in the value range from 100 to 1000 Ω/sq in conjunction with thedescribed embodiment. Contacts 11, 12 are fitted in the normal way tothe ends of the polysilicon strip 10 and are connected to lines 13, 14,which are in turn connected to the connections of a controllable currentsource 15.

[0049] The response of the differential resistance and of thecurrent/voltage characteristic of the polysilicon strip 10 for the firstembodiment of the operating method according to the invention areillustrated in FIG. 2.

[0050] During operation, the controllable current source 15 makes itpossible to provide the polysilicon strip with a reversible response,with the polysilicon strip having a first differential resistance Rdiff1up to a current limit value It corresponding to an upper voltage limitvalue Vt, and having a second differential resistance Rdiff2, which isless than the first differential resistance Rdiff1, at current levelsabove this.

[0051] As can clearly be seen from FIG. 2, this response is the same asthe response of a known DIAC. In particular, all that need be rememberedis that the current may be limited to a critical upper current value Ik,above which irreversible changes occur in the polysilicon, for examplefused channels.

[0052] Typical test conditions for the controllable current source 15illustrated in FIG. 1 are pulse measurements in the 100 nanosecondrange, with the polysilicon strip 10 being observed to have recoverytimes for reaching the higher resistance, starting from the lower one,in the millisecond range.

[0053] The switching of the resistor in the form of the polysiliconstrip 10 can be explained by the current limit value It being exceededsuch that this leads to the resistor being flooded with charge carriersby means of thermal generation. Analytically, this switching can bedescribed by a specific electrical power Vt×It being supplied in aspecific resistor volume b×l×h, where b, h, l are the above-mentioneddimensions of the polysilicon strip 10.

[0054] The definition$\frac{V_{t} \times I_{t}}{l \times b} = {k = {constant}}$

[0055] and the definition of the sheet resistance Rsq by$R = {{Rsq}\frac{l}{w}}$

[0056] results in the relationship $\begin{matrix}{{Vt} = {{Rb}\sqrt{\frac{k}{R_{sq}}}}} & (1)\end{matrix}$

[0057] In this case, the voltage limit value Vt can be varied by thewidth of the polysilicon resistor, the resistance R and by the specificresistance or resistivity. R is normally governed by the application,and the minimum width b of the resistor is governed by theelectromigration requirements and/or the maximum current carryingcapacity.

[0058] Virtually any desired resistance from a few ohms up to theMegaohm range can be achieved, with an acceptable surface area, by thecombination of different resistor dopings in polysilicon or by usingdiffusion resistors (for example n+/n−/intrinsic) so that the limitvoltage Vt can be varied over a very wide range.

[0059]FIG. 3 shows a current/voltage characteristic with two selectedresistors, with the same nominal resistance. The curve (1) shows theresponse for a ratio b/l=5/1, and the curve (2) shows the response for aratio b/l=25/5. It can clearly be seen that the limit voltage Vt2becomes greater as the width l increases, that is to say Vt2=13.8 V isgreater than Vt1=4 V.

[0060]FIG. 4 shows the arrangement of a polysilicon strip in order toexplain a second embodiment of the operating method according to theinvention.

[0061] According to this second embodiment, the polysilicon strip 10 isformed from a number of strip elements 10 a-10 d, which have differentdoping and/or a different length 11-14, so that a predetermined voltagelimit value Vt can be achieved over a wide value range by appropriateseries connection. Such connection can be achieved by means of the fuseprinciple, by laser trimming, or by other conventional techniques.

[0062]FIG. 5 shows a radio-frequency circuit arrangement in order toexplain one field of application of the operating method according tothe invention.

[0063] In FIG. 5, 100, 200 respectively denote a first and a secondsupply voltage line. E1 to E6 are ESD protective elements, for exampletrigger diodes, which are provided between the two supply lines. A1, A2are, respectively, a first and a second radio-frequency path forinjection of a radio-frequency signal, and they are respectivelyconnected to the circuit nodes K1 and K4, which in turn form centernodes for the ESD protective elements E1, E2 and E3, E4, respectively.

[0064] A differential stage, which is denoted by DS and has two inputtransistors T1, T2 and one output transistor T3, is provided in thecenter of the circuit. Further details of this differential stage areknown and will not be explained in any more detail here. 50 Ω resistorsR1 and R2 are provided as bias resistors for the differential stage DSand are connected via the respective circuit nodes K2 and K3 to thetransistors T1, T2. Furthermore, the nodes K2, K3 are at the samepotential as the respective nodes K1 and K4.

[0065] The particular difficulty of ESD protection in a radio-frequencycircuit arrangement such as this is the very small tolerable capacitanceplates which can be used for ESD protection. Until now, effective ESDprotection has is been impossible to achieve in many cases. The use ofthe polysilicon strip 10 according to the invention as a switchableresistor allows these previous problems to be overcome.

[0066] For this purpose, the resistors R1, R2 are simply each replacedby a polysilicon strip according to the invention and of appropriatesize, in which case the ESD protective elements E1 and E3 may be omittedat the same time. Since the parameters of the width d and the resistanceR of these resistors can be varied independently of one another, it ispossible, as shown in FIG. 4, to design a 50 Ω resistor with a specificb/l ratio, which has a suitable limit voltage Vt2, for example ofseveral hundred volts, which is suitable for this application.

[0067] A suitable layout thus allows the polysilicon strip 10 to be usedas the resistor R1 or R2, and at the same time as the ESD protectiveelement E1 or E3, respectively. This leads to a significant saving insurface area, and at the same time to improved performance, since thereis no need for any additional capacitance plates in the form ofadditional ESD protective elements E1, E2.

[0068] A resistance layer of p+ polysilicon with 310 Ω/sq will be usedas a specific example for the design of a polysilicon resistor strip ina radio-frequency circuit arrangement 50 as shown in FIG. 5. Forelectromigration reasons, b must be greater than 15 micrometers. Withthe relationship (1) quoted above, b is 20 micrometers, so that theelectromigration condition is satisfied, and an ESD resistance ofapproximately 1 kV is achieved. Should greater widths b be requiredowing to electromigration or ESD protection, the sheet resistance may beincreased by changing the doping.

[0069] Although the present invention has been described above on thebasis of preferred exemplary embodiments, it is not restricted to these,but may be modified in a large number of ways.

[0070] In particular, the present invention is not restricted topolysilicon or to a specific type of polysilicon doping. In addition,the quoted applications are only by way of example and may be extendedas required to any fields of application where switchable resistors arerequired.

[0071] The strip may also have any other desired geometries.

[0072] Typical further fields of application for the method according tothe invention are:

[0073] a. nonlinear pulse shaping of high-speed current pulses, forexample in laser diode drivers;

[0074] b. fields of application of a DIAC, for example triggering ofTRIACs and thyristors for high-current/high-voltage and smart powerapplications;

[0075] c. non-destructive dissipation of high-current pulses, forexample of electrostatic discharges (ESD protective elements), lightningprotection circuits;

[0076] d. latch-up protection circuits;

[0077] e. applications in the high-current field, in which the powerloss is intended to be limited for high current densities.

[0078] List of Reference Symbols

[0079]1 Wafer substrate

[0080]5 Insulation layer

[0081]10; 10 a-d Polysilicon strip

[0082]11, 12 Contacts

[0083]13, 14 Lines

[0084]15 Controllable current source

[0085]1,11-14,b,h Length, width, height

[0086] It; Vt, Vt1, Vt2 Current limit value; voltage limit value

[0087] Ik Critical current value

[0088]100, 200 Supply potential lines

[0089] VDDP, VSSB Supply potentials

[0090] E1, E6 ESD protective elements

[0091] A1, A2 Radio-frequency pads

[0092] R1, R2 50 ohm bias resistors

[0093] DS Differential stage

[0094] K1-K4 Circuit nodes

What is claims is:
 1. Operating method for a semiconductor componenthaving: a substrate; a conductive strip which is applied to thesubstrate; a first and a second electrical contact, which are connectedto the conductive polysilicon strip such that this forms an electricalresistance in between; with the semiconductor component being operatedreversibly in a current/voltage range in which it has a firstdifferential resistance (Rdiff1) up to a current limit value (It)corresponding to an upper voltage limit value (Vt) and, at currentvalues greater than this, has a second differential resistance (Rdiff2),which is less than the differential resistance (Rdiff1).
 2. Methodaccording to claim 1, characterized in that the strip has a sheetresistance which is in the range between 100 and 1000 ohms per square.3. Method according to claim 1, characterized in that the strip has acuboid shape with a length l, a width b and a height h.
 4. Methodaccording to claim 1, characterized in that the strip is formed from anumber of strip elements with different dopings and/or lengths, with thestrip elements being combined in series so as to produce a predeterminedvoltage limit value (Vt).
 5. Method according to claim 4, characterizedin that the strip elements are alternately p-doped and n-doped. 6.Method according to claim 5, characterized in that the alternate dopingcreates additional diode forward-bias thresholds in the current path. 7.Method according to claim 5, characterized in that the alternate dopingcreates additional diode breakdown thresholds in the current path. 8.Method according to one of claim 3, with the voltage limit value Vtbeing set in accordance with the relationship Vt=R b(k/Rsq)½, where R isthe resistance, b is the width, k is a constant and Rsq is the sheetresistance of the strip.
 9. Method according to claim 1 wherein, withthe semiconductor component is used as an ESD protective element. 10.Method according to claim 9, with the semiconductor component being usedwith two functions, as an ESD protective element and as a bias resistor,in a radio-frequency circuit arrangement.
 11. Method according to claim1, with the strip being formed from doped polysilicon as thesemiconductor material.